Process for the pyrolysis of hydrocarbons to acetylene



Feb. 4, 1958 F. F. A. BRACONIER ET AL 2,

PROCESS FOR THE PYROLYSIS OF HYDROCARBONS TO ACETYLENE Filed Feb. 8, 1955 United States Patent 2,822,411 PROCESS FOR THE PYROLYSIS 0F HYDRO- CARBONS T0 ACETYLENE Frederic Frangois Albert Braconier, Plainevaux, and Armand Hubert Auguste 'Delsemme, Ougree-Sclessin, Belgium, assiguors to Societe Belge de lAzote et des Produits Chimiques du Marly, Liege, Belgium, a company of Belgium Application February 8, 1955, Serial No. 486,895 Claims priority, application Belgium July 15, 1954 '1 Claim. (Cl. 26tl-679) The present invention relates to aprocess for the pyrolysis of hydrocarbons and to apparatus for carrying out this process for the purposes of preparing unsaturated hydrocarbons, including particularly acetylene.

It is known that acetylene can be produced by heating gaseous hydrocarbons or liquid hydrocarbons atomized into finely divided particles .at temperatures of the order of 1000 to 2000 C. for .a very-short time.

It is also known that, to bring the hydrocarbons to be pyrolysed to the required temperature, it is possible to introduce them into the still hot gases .ofcombusion of a flame of a burner, fed with a gaseous or liquid fuel, and substantially concentrated oxygen, and that in order to promote the subsequent concentration of the acetylene formed, it is desirable to introduce the smallest possible quantities of inert gases into the gas of pyrolysis, with the combustion gases. To this end, the burner can be fed with oxygen containing a minimum of other gases,

notably nitrogen, on the one hand, and with fuel of high hydrogen content (for example substantially pure hydrogen, or methane or coke-oven gas), on the other hand,

the steam formed by the combustion of the hydrogen be ing eliminated from the gases by condensation.

However, such operating conditions, which-involve very high temperatures in places, give rise to particular problems from the viewpoint of the resistance of the materials of which the burners are constructed, and these problems cannot readily be solved.

In order "to overcome these difiiculties, it has already been proposed, for example in United States Patent No. 1,823,503, to produce a disc of flames converging toward the center of the burner, which are thus held at a distance from the walls of the combustion chamber, and to cause the hydrocarbons which are to be pyrolysed to penetrate perpendicularly to these flames.

In accordance with another United States Patent No. 2,343,866, the hydrocarbons are brought into contact with the flame in countercurrent, this device having the disadvantage of necessitating combustion chambers consisting of refractory materials.

The object of the present invention is the pyrolysis of hydrocarbons to produce a highpercentage of unsaturated hydrocarbons, particularly acetylene.

A further object is to produce acetylene without employingexcessively'high temperatures which would detrimentally effect the burners and other parts of the apparatus.

A still further object is -to avoid the and the deposition .of carbon.

Another object is the provision of apparatus for efficiently pyrolyzing coke oven gas and other hydrocarbons to form unsaturated hydrocarbons.

According to the present invention there is provided a process for the pyrolysis of hydrocarbons to form unsaturated hydrocarbons, particularly acetylene, wherein a hyformation of soot drocarbon, .or a mixture of hydrocarbons, is introduced transversely into the hot gases of combustion of a flame duction taking place in a pyrolysis chamber and the flame having a high oxygen and hydrogen content, the intr0-.

, 2,822,411 Patente-cl, Feb. 4, 1958 2 being formed in a combustion chamber, both chambers having metallic walls which are externally cooled by the circulation of cold water.

Preferably the combustion chamber is vertically disposed and is extended as a conduit to form a pyrolysis chamber, the combustion chamber widening in'the downward direction. The hydrocarbons to be pyrolysedare injected into the current of hot gases of combustion.

The hydrocarbons to be pyrolysed are injected at such an angle and velocity as to cause them to penetrate substantially perpendicularly to the axis of the current of-hot gases, at a predetermined level, at which the combustion of the hydrogen is substantially complete. The pyrolysis thus takes place under the action'of the high temperature produced by the superheated steam resulting from the combustion. The gas mixture consisting of the gases of pyrolysis and of combustion is then quenched by a transversely directed water spray at a predetermined distance from the level at which the hydrocarbons to be pyrolysed are injected.

By operating in this manner, it is possible to avoidsubstantially all formation of soot and deposition of carbon, because the oxidising effect of the superheated steam is more closely related to the nascent carbon than to the acetylene produced.

Moreover, because of the condensation of the water after pyrolysis, which water forms the greater part of the combustion gases, high acetylene concentrations'can be produced in the gas after pyrolysis.

The invention is also concerned with an apparatus comprising a substantially vertically disposed combustion chamber extended at its lower end into the form of 'a conduit, forming a pyrolysis chamber for receiving the gases of combustion, the two chambers having metal walls and being surrounded by a jacket through which cooling water may be circulated, injecting means at the upper end of the combustion chamberthroughwhichaninflammable mixture of a fuel and a combustion assisting agent may be admitted to the combustion chamber, an injection system including one or more circles of orifices disposed around the periphery of the-pyrolysis chamber for centripetal injection of the hydrocarbon or hydrocarbons to 'be pyrolysed, said system being-located in :a zone of the pyrolysis chamber beyond that which is occupied by the flame produced from the combustion gases, in the use of the apparatus, but in which the temperature is still favorable to the formation of unsaturated hydrocarbons, and the apparatus further comprising a system for the transverse introduction of water into the pyrolysis chamber,'beyond the pyrolysis zone, where the composition of the gas mixture attained in the pyrolysis zone is still substantially unchanged.

For abetter understanding of the invention and to show how the same may be carried into effect, reference will now'be'made to the accompanying drawings, in which Figure 1a is a diagrammatic sketch illustrating a vertical section through one embodiment of an apparatus.

Figure lb is a horizontal section on the line XX of Figure la'.

Figure 2a is a view similar to Figure la, of a second embodiment, and

Figure 2b is a horizontal section on the line YY of Figure 2a.

Referring first to Figures 1a and 1b, fuel e. g. hydrogen, methane or coke-oven gas can-befed to a tube 1 and oxygen (or air highly enriched in oxygen) fed to a tube 2, these being mixed in suitable proportions for the complete combustion of the gaseous fuel. The mixed gases can be introduced through an injector 3 into a combustion chamber 4, in which the mixture is ignited. The flame formed reaches a particular length therein, beyond which r 3 the hot combustion gases will be composed principally of superheated steam and, to a minor extent, of nitrogen and oxides of carbon. At a particular distance from the injector 3, beyond the zone in which the flame ceases to exist at which distance the current of gases of combustion comprises a zone in which the optimum temperature obtains, for example 2000 C. the combustion chamber 4 is continued in a conduit 5 which forms a pyrolysis chamber.

The conduit 5 has an associated ring 6 or other annular distributing device for the injection, through a number of nozzles 7 leading to the orifices 7a, of the liquid hydrocarbon to be pyrolysed (preferably in a finely divided state) or the gaseous hydrocarbon in a direction perpendicularly to the gases of combustion, the hydrocarbon to be pyrolysed being fed to the ring 6 through the conduit 8. The intimately mixed gases of combustion and pyrolysis produced are quenched at a predetermined distance from the pyrolysis zone by the injection of cold water through the atomizer 9 in a direction transverse in relation to the current of gases. In order to protect the metal walls of the combustion chamber 4 and of the conduit 5 from the effects of heat, they are surrounded by a water-circulation jacket 10 extending to beyond the pyrolysis zone situated on the downstream side of the ring 6. The circulation of water around the metal walls of the combustion chamber 4 and of the conduit 5 not only preserves these walls from the harmful effects of the heat evolved in combustion, but also eliminates or very greatly attenuates any catalytic efiect of the metal of the walls on the reacting gases.

Figure 1b shows the arrangement, around the conduit 5 of the nozzles 7 through which the hydrocarbon to be pyrolysed is fed to the orifices 7a'opening into the pyrolysis zone. The said nozzles 7 are advantageously so oriented as to permit very good penetration of the products to be pyrolyzed in a direction perpendicular to the direction of the gases of combustion.

The embodiment shown in Figures 2a and 2b is particularly useful for the construction of industrial furnaces of high capacity. The reaction zone in which the hydrocarbons to be pyrolysed are injected into the hot gases of combustion of the flame, consists of a space of annular cross-section, the outer and inner walls of which each comprise, along their peripheries, a circle or circles of distribution orifices disposed to face towards each other.

By thus directing the jets of hydrocarbons to be treated perpendicularly to the gases of combustion and one against the other, good mixing of the reacting gases is obtained by the interpenetration of the gaseous currents, which arrive simultaneously from three difierent directions. In Figures 2a, and 2b, the references 1 to 10 designate the same parts as in Figures la and lb, but the hydrocarbons to be treated also fed through a conduit 8 to a central 4; distributor 6' and the accessory parts thereof are also provided with a water-circulation cooling system.

The distance between the injector 3 and the distributor 6 for the hydrocarbon to be pyrolysed, on the one hand, and the said distributor 6 and the atomiser 9 on the other hand, depends upon many factors, including inter alia the dimensions. of the apparatus, the nature of the combustible gases and combustion-supporting agents and of the hydrocarbons to be pyrolysed, the rate of flow, the pressure and temperature at which these various gases are injected and the direction in which the hydrocarbon to be pyrolysed is injected. It is possible to determine these distances empirically for each particular case and to design or arrange the apparatus accordingly. In order that a given apparatus may be readily adapted to varying operating conditions, it is possible notably to dispose these various elementsin such manner that they comprise, for example, a fixed device 6 for the distribution of hydrocarbons to be pyrolysed and a movable injector 3 and a movable atomiser 9, the positions of which are adjustable in the direction of the axis of the apparatus.

The following examples illustrate the use of the described embodiment of the apparatus for the pyrolysis of various gaseous or liquid hydrocarbons.

EXAMPLE I Pyrolysis of a methane fraction A flame was produced by feeding to the injector 3 a mixture of 57 m. /h. of coke-oven gases and S9 m. /h. of oxygen. 110 m. /h. of a rich gas having a high methane content were passed into the distributor and 212 m. h. of mixed gases of pyrolysis and of combustion were obtained. The gases before and after combustion had the composition (in percent by volume) indicated in the following table.

Pyrolysis of an ethylene fraction A flame was produced by means of 58 m. /h. of cokeoven gases and 64 m. /h. of oxygen. 113 m. /h. of a fraction of ethylene gas were fed to the distributor and gave 251 m. h. of mixed gases of pyrolysis and of combustion. The composition of the gases (in percent by volume), before and after pyrolysis, is indicated in the following Table II.

TABLE H OH; 0111a 0111: 01H; 01 C0 0: H: N:

113 mfi/h. of crude gas..- 43.2 12.6 1.6 35.8 0.8 0.6 6.4 1.2 3.8 251 1113/11. of pyrolysed a gas 14.2 1.0 9.4 6.0 0.4 21.2 5.2 37.0 5.6

EXAMPLE 111 By feeding coke-oven gas into the flame at the same rates of flow as in the preceding examples and by injecting l./h. of gas oil by ,atomisation, m. /h. of gas of pyrolysis having the following composition (in percent by volume) were obtained.

CH4 CaHu 02H: 01114. O: .00 CO1 H: N!

180 mfi/h. of pyrolysed gas What we claim is:

A process for the pyrolysis of hydrocarbons to acetylene comprising forming a flame in an open combustion zone of increasing cross-section in the direction of flow of the gases from the flame, radially injecting a plurality of streams of hydrocarbons into the hot gases from said flame at a second zone wherein combustion is substantially complete, said plurality of streams emanating from a plurality of locations spaced circularly about said secend zone and lying substantially in a plane transverse to the flow of hot gases from said flame, injecting a plurality of streams of hydrocarbon radially outwardly from a location adjacent the center of the hot gases from said flame and lying in said transverse plane, subjecting the exterior of said combustion and said second zones to external water cooling and thereafter quenching the gases at a point beyond said zone of hydrocarbon injection.

References Cited in the flle of this patent UNITED STATES PATENTS 2,195,227 Sachsse Mar. 26, 1940 2,498,444 Orr Feb. 21, 1950 2,664,450 Sachsse et a1 Dec. 29, 1953 2,672,488 Jones Mar. 16, 1954 2,680,706 Kilpatrick June 8, 1954 2,692,903 Hachmuth Oct. 26, 1954 2,719,184 Koshbahn et al Sept. 27, 1955 FOREIGN PATENTS 895,444 Germany Nov. 2, 1953 

